The present invention is in a process of burning animal waste and more specifically in a process for burning cattle dung.
Large herds of cattle kept in confined spaces produce a large quantity of cattle droppings, which must be disposed of from time to time. Depending on the nature of the feed, the cattle dung has a relatively high content of alkalies and chlorine making it unsuitable for use as fertilizer and presenting a disposal problem.
U.S. Pat. No. 3,864,458 discloses a process of incinerating aqueous organic waste which have a high content of chlorine as alkali metal chlorides or alkaline earth metal chlorides. Such waste sludges are formed, e.g., in municipal clarifying plants, in refineries or as ballast water of tankers. The combustion is effected at a temperature of 621.degree. to 788.degree. C. in a stationary fluidized bed in the presence of added sulfur compounds and, if desired, in the presence of added fuel. Sulfur is added to avoid bed defluidization. The sulfur is added in a form available for reaction with chlorides, such as H.sub.2 SO.sub.4, in order to cause most or all of the chlorine content to be volatilized as HCl, so that the formation of low-melting alkali chlorides or of low-melting eutectics will be avoided. HCl must be removed from the exhaust gases by scrubbing with CaCO.sub.3 or lime. This technique produces large quantities of substances which present another disposal problem. The high HCl concentrations give rise to severe corrosion problems in the succeeding gas processing equipment requiring replacement or expensive and exotic construction materials and fabrication techniques. Thus, the process of this patent results in a disposal problem and is plagued with variable economics.
U.S. Pat. No. 3,907,674 teaches that the presence of other elements, such as magnesium, in the process of U.S. Pat. No. 3,864,458 results in formation of low-melting eutectic mixtures. The formation of such mixtures results in the defluidization of the fluidized bed, even if the process is so controlled that the chlorine content is completely volatilized as HCl, the alkali metals are completely converted to sulfates and the combustion is effected at a temperature in the range of from 620.degree. to 787.degree. C., below the volatilization temperature of the alkali chlorides. For that reason U.S. Pat. No. 3,907,674 recommends modifying the process so that the combustion of the aqueous waste stream is effected at temperatures of from 800.degree. to 1000.degree. C. in the presence of sulfur or sulfur-containing compounds, of added fine-grained SiO.sub.2 having a particle size below 44 .mu.m and of at least one added metal oxide of the group CaO, MgO, Al.sub.2 O.sub.3 and Fe.sub.2 O.sub.3. As a result, a considerable part of the alkali chlorides is volatilized and discharged with the exhaust gas and the remainder combines with the metal oxides to form high-melting crystalline alkali compounds. But the volatilized alkali chlorides give rise to corrosion problems in the succeeding gas processing system equipment, and to a formation of deposits and crusts in steam boilers and gas purifiers, i.e., to serve disturbances in operation.